Process of shrinking polyvinyl alcohol fibers and acetylizing with mixture of mono-and di-aldehydes and product thereof



United States Patent PROCESS OF SHRINKING POLYVINYL ALCOHOL FIBERS AND ACETYLIZING WITH MIXTURE OF MONO- AND DI-ALDEHYDES AND PRODUCT THEREOF Edward T. Cline, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application September 18, 1952, Serial No. 310,360

6 Claims. (Cl. 8-1155) This invention relates to a process for improving the properties of polyvinyl alcohol fibers.

It is known that filaments of hydroxylated polymers such as polyvinyl alcohol or hydrolyzed copolymers of vinyl esters with minor amounts of polymerizable vinyl or vinylidene compounds can be oriented by drawing to yield fibers of high tensile strength. These oriented fibers have many important advantages such as insolubility in most organic solvents and high softening point. However, they are characterized by undesirable sensitivity to water, particularly hot Water. Moreover, these fibers lack the resilience necessary for the production of satisfactory fabrics. This latter disadvantage is observed even with fibers of hydroxylated polymers which have been treated so as to decrease or eliminate Water sensitivity, either chemically, as described in application Ser. No. 142,538, filed by McClellan and Stevenson on February 4, 1950, which issued as U. S. Patent 2,636,804 on April 28, 1953, or physically, as described in application Ser. No. 157,634, filed by Cline, Pinkney, Plambeck and Stevenson on April 22, 1950, which issued as U. S. Patent 2,610,360 on September 16, 1952.

It has been proposed to treat polyvinyl alcohol fibers with aldehydes such as formaldehyde, butyraldehyde or crotonaldehyde for various purposes. When such treatments are carried out to as near completion as possible, there results a completely or substantially completely acetalized product which no longer possesses the properties of polyvinyl alcohol, in that it has a much lower softening point and the fibers cannot be stabilized against shrinkage in boiling water if oriented to improve strength. When the reaction is only partial, the products heretofore described have been characterized by low work recovery in the fiber form and, in fabrics, by poor resilience characteristics such as low crease resistance and low recovery from crease.

Attempts have also been made to produce resilient polyvinyl alcohol fibers by partial acetalization of the polyvinyl alcohol in bulk form with such cyclic aldehydes as benzaldehyde, followed by spinning the partial polyvinyl acetal from an organic solution and stretching the fiber. However, it has been found that the oriented fibers so obtained shrink very badly in boiling water. Moreover, attempts to apply to these fibers a heat treatment to reduce their shrinking tendencies fail because the fibers stick at the required temperature, or if the temperature is lowered, the excessive shrinkage in water is not prevented. Even a formaldehyde treatment does not give adequate water resistance to fibers obtained by spinning partial acetals of polyvinyl alcohol with cyclic aldehydes. A new method of preparing resilient polyvinyl alcoholpolyvinyl acetal fibers has recently been proposed in application Ser. No. 142,537, filed on February 4, 1950, by Cline and Stevenson, which application issued April 28, 1953, as U. S. Patent 2,636,803. This consists in relaxing a dry, oriented polyvinyl alcohol fiber to a controlled degree in a nonsolvent medium at high temperature, e.- g.

210-245 C., swelling the heat-set fiber in an aqueous bath at a temperature above 60 C., drying the swollen fiber and finally subjecting it to partial acetalization with a monoaldehyde wherein the aldehyde group is directly attached to annular carbon of a cyclic structure of at least five atoms. This method gives excellent results in that it leads to fibers of high resilience and superior resistance to water. However, it requires accurate control of the high temperature relaxing treatment to avoid possible discoloration and weakening of the fiber, and further accurate control of the subsequent aqueous treatment at relatively high temperature, which may lead to sticking and deterioration of the fibers.

This invention has as its object the preparation of polyvinyl alcohol fibers of outstanding resistance to hot water 7 and insolubility in most organic solvents, of high Work recovery in fiber form and superior resilience in fabric form, and of excellent resistance to shrinkage in boiling Water. A further object is the provision of a more readily controllable process for obtaining such fibers. Other objects will appear hereinafter.

These objects are accomplished by the process of the present invention wherein an oriented polyvinyl alcohol filament is subjected to a treatment comprising (1) relaxing the oriented fiber by immersion in an aqueous bath having substantially no solvent action thereon under such conditions of water content, temperature, and time, as indicated below, that the filament shrinks by at least 25%, but not more than of its initial length, i. e., shrinking the oriented fiber by contact with a nonsolvent aqueous liquid of at least 30% and preferably of at least 75% Water content preferably at a temperature between 0 and 50 C. for a time sufficient toshrink the fiber between 25 and 50% of its initial oriented length, and (2) reacting the relaxed filament with a mixture of a monoaldehyde wherein the aldehyde group is directely attached to an annular carbon of a cyclic structure of at least five atoms and a minor amount, between 3% and 20% of the weight of the monoaldehyde, of a dialdehyde of at least three carbon atoms until at least 25%, but not more than 60%, of the hydroxyl groups in the polyvinyl alcohol have been acetalized.

The process of this invention is applicable to oriented fibers of macromolecular, synthetic, linear hydroxylated polymers consisting essentially of vinyl alcohol,

units. Preferably, the fiber to be treated consists solely of polyvinyl alcohol, but the latter can also contain very minor proportions, i. e., below 5% and preferably below 2% by weight, of another vinylidene polymer whose presence in such low amounts does not substantially modify the characteristics of polyvinyl alcohol. For example, commercial polyvinyl alcohol sometimes contains low proportions of the nonhydrolyzed ester, e. g. polyvinyl acetate, from which it is prepared. There can also be used hydrolyzed copolymers of vinyl esters with very low proportions of vinylidene compounds such as ethylene, methyl methacrylate, and the like.

By oriented fiber is meant, as usual, a fiber which has been drawn under tension to an extent such that it shows a typical fiber X-ray diffraction pattern. In general, oriented fibers are obtained when the polyvinyl alcohol filament polymer is stretched at least 300% of its initial length. Polyvinyl alcohol filaments can be drawn in a hot salt bath, e. g. a boiling concentrated solution of sodium dihydrogen phosphate; or they can be drawn in hot oil, or in air at temperatures between 200 and 250 C. In general, the filament is drawn to the maximum length short of the breaking point, e. g. with a draw ratio between 3:1 and 11:1, depending on the filament and the drawing conditions. Preferably, however, the filament is drawn to a draw ratio in the range of 3.5:1 to 5.5:] in a hot salt bath as part of the wet spinning operation. With higher draw ratios, it may be necessary to increase shrinkage of the filament in the aqueous relaxing bath to more than 50% of the oriented length. This drawing operation increases the tensile strength of the filament considerably. "arious methods of preparing oriented polyvinyl alcohol fibers have been published.

By macromolecular is meant a polymer having a degree of polymerization, i. e., a number of recurring units, of at least 100, and preferably at least 250 for best fiber properties.

Spinning of the polyvinyl alcohol into filaments may be accomplished by any of the known methods including dry or evaporation spinning. Wet spinning into an aqueous salt bath, e. g. a concentrated sodium dihydrogen phosphate bath, is a preferred method. The fiber may then be oriented by stretching in a hot salt bath, followed by Washing and drying at fixed length to prevent shrinkage and I sticking of the filaments; or it may be partially stretched in air or in a liquid medium at ordinary temperature, followed by washing, drying at fixed length and finally stretching in air or a nonsolvent liquid medium at ZOO-240 C. to complete the orientation.

It has been observed that better results are frequently obtained by allowing the oriented, dry filament to undergo a conditioning stage prior to the first step of the treatment, by letting it stand at room temperature for at least 24 hours. This conditioning however, is by no means essential.

The oriented fiber is then subjected to the first step of the process of this invention, which is a relaxing treatment in an aqueous nonsolvent bath under such conditions that shrinkage of the filament, to the extent of at least 25% and not more than 50% of its initial (oriented) length, takes place. Since polyvinyl alcohol filaments at this stage can be dissolved or undesirably softened by water, particularly at elevated temperatures, the water content and temperature of the relaxing bath and time of treatment must be adjusted in relation to one another to achieve the desired result, which is a shrinkage of the oriented filament within controlled limits. The filament shrinkage increases as the water content and temperature are increased. As the water content and temperature are increased the time required is decreased. Generally there is an induction period which may involve several minutes during which no visible shrinkage occurs. Thereafter shrinkage occurs rapidly and in many cases soon reaches or approaches an end point. Further soaking does not produce appreciably more shrinkage. The ranges for the water content, temperature, and time, are interdependent variables. In general the relaxing bath should comprise at least 30%, and preferably at least 75% of water. It can consist entirely of water, and for economic reasons this is obviously desirable, provided the temperature and time of contact are so adjusted that no appreciable solvent action on the filament takes place. Shrinkage increases with increased time and also with increased temperature. The denier is of no substantial importance in the textile size range, i. e., deniers of l6. For larger filaments and bristles, longer soaking in the relaxing baths is necessary to permit equilibrium penetration of the bath and consequent homogeneous and reproducible shrinkage of the polymeric structure. Besides water itself, suitable baths include those containing up to 70%, preferably up to 25%, of a water-miscible liquid of one to ten carbon atoms, such as an aliphatic alcohol, acid, ester, ether or ketone. Specific liquids of these classes include methanol, ethanol, acetic acid, ethylene glycol, tetraethylene glycol, fl-methoxyethyl acetate, dioxane, dimethoxytetraethylene glycol, acetone and the like.

The effects of changes in water content and of temperature are illustrated in the table below wherein DEG is diethylene glycol (of the indicated concentration in water).

The temperature of the relaxing bath can vary between just above the freezing point and just below the boiling point of the aqueous medium, subject again to the requirement that no solvent action or no appreciable softening action is exerted on the filament. Preferably, it is between 0 and 50 (1., and still more preferably between 10 and 30 C. The time of contact need only be that sufiicient for the filament to shrink between 25 and 5 0% of its initial length. Depending upon the other conditions, and also in part upon the size (denier) of the filament, it can vary from a very short period, such as about three seconds when the operation is done continuously, to about twenty minutes. The desired shrinkage can be brought about simply by immersing the oriented filament in the bath in the absence of any tension, e. g., in skeins or loose form until the filament has shrunk to the desired degree; or a controlled tension may be applied on the filament, for example, by running it between two rollers of which the second, or collecting one, rotates at a lower speed than the first. In this manner the operation is continuous and a predetermined degree of shrinkage is achieved.

Between the first and the second step of this process, there may optionally be applied to the filament a drying operation whereby the superficial water is removed, e. g. by air drying or by displacement with a water-miscible organic solvent such as ethanol. This operation produces a dry filament for use in the subsequent acetalization step, but it is not essential since the acetalization bath can tolerate a certain amount of water, as will be discussed below.

The second and last step of the process is the partial acetalization of the fiber with a mixture of a cyclic monoaldehyde having the aldehyde group directly attached to annular carbon and, in minor amounts, a dialdehyde of at least three carbon atoms as such or as a compound bydrolyzable thereto in situ, i. e., a dialdehyde precursor including, for example, acetals and hemi-acetals of dialdehydes, and cyclic anhydrides of dihemiacetals of dialdehydes. The latter compounds may also be regarded as alpha, omega-dialkoxy cyclic ethers, i. e., cyclic ethers wherein the two alkoxy substituents are on the two carbons directly bonded to the ether oxygen, both of such carbons also carrying a single hydrogen atom. An example of this type of compound is 2,5-diethoxytetrahydrofuran, which hydrolyzes readily to succindialdchyde. Examples of both the cyclic monoaldehyde and the dialdehyde or potential dialdehyde will be given as the description proceeds. The dialdehyde or potential dialdehyde, which presumably functions as a cross-linking agent,

need be used only in minor amounts relative to the cyclic monoaldehyde, suitably from 3 to 20%, and preferably from 5 to 15% by weight thereof.

The acetalization treatment may be carried out in the absence of a solvent if enough of the cyclic monoaldehyde is used to insure good contact with the yarn, but the use of the aldehyde without solvent frequently causes excessive shrinkage during the treatment. The acetalization is preferably carried out in a carbonyl-free, liquid, organic medium which is a solvent for the aldehyde and, of course, a non-solvent for the polyvinyl alcohol fiber. This medium is preferably a monohydric or dihydric alcohol or ether-alcohol of one to six carbon atoms, e. g. methanol, ethanol, propanol, butanol, hexanol, glycol, diethylene glycol, methoxyethanol, butoxyethanol, etc.; but it may be any other non-oxo solvent such as dibutyl ether, tetrahydrofuran, dioxane, diethylene glycol diethyl ether, and the like. The reaction system need not be anhydrous. It can tolerate some water, and, in fact, addition of water in some cases increases the rate of acetalization. However, with most cyclic aldehydes there should preferably be present not more than still more preferably not more than 5% of water, based on the weight of the total acetalization mixture. An excessive amount of water tends to cause undesirable additional shrinkage of the filament.

The relative proportions of polyvinyl alcohol and monoaldehyde are not critical provided there is sufficient aldehyde to react with at least of the hydroxyl groups. The monoaldehyde is normally used in the proportions of one-fourth to four moles per mole of polyvinyl alcohol, and preferably one-half to three moles per base mole of polyvinyl alcohol. The base mole of a polymer such as polyvinyl alcohol is the unit weight of the recurring unit (Bawn, The Chemistry of High Polymers, page 173), in this case the CH2CHOH unit. The reaction temperature is desirably at least 50 C. and it can be as high as desired short of decomposition of the reactants, a generally useful range being between 70 and 150 C. The reaction is carried out until at least 25%, and preferably at least of the hydroxyl groups in the polyvinyl alcohol have reacted, but it should be stopped before more than about 60% and in most cases before more than about 50% of the hydroxyl groups have reacted. It will be apparent that the required degree of acetalization can be varied considerably, depending upon the reactivity and molecular weight of the aldehyde employed. However, it has been found that the limits indicated above lead to satisfactory products. The desired end point is determined by measuring the increase in weight of the fibers as a result of the acetalization and simply calculating therefrom the percentage of hydroxyl groups reacted.

Any of the usual acetalization catalysts can be employed including phosphoric acid, sulfuric acid, ammonium chloride, sodium bisulfate, calcium chloride, zinc chloride, ferric chloride, oxalic acid, maleic acid, citric acid, boron trifluoride, p-toluenesulfonic acid, and the like. The catalysts are present in the solution to the extent of 0.05% to about 10% by weight, a preferred range of proportions being from 0.5 to 5%. In general, the acetalization treatment requires from about ten minutes to twenty hours, depending among other things on the aldehyde used and on the extent of acetalization desired, but under favorable conditions of temperature and concentration it can be carried out in five minutes or even less. During this treatment, the polyvinyl alcohol fiber shrinks somewhat more and it gains weight.

Optionally, the acetalization step is followed by washing with water and/or weak alkali such as sodium bicarbonate or ammonia to neutralize any acid present, and by a boil-off treatment with water, with or without a detergent. If desired, these two operations may be combined by boiling the yarn with a dilute, e. g. 0.l1%, solution of sodium hydroxide or sodium carbonate.

The process of this invention gives an oriented polyvinyl alcohol-polyvinyl acetal fiber in which between 25 and 75% of the hydroxyl groups are acetalized by av cyclic aldehyde of the type defined above and a difunctional aldehyde as above defined. Otherwise expressed, the ratio of acetal groups to hydroxyl groups is between 1:6 and 120.66. These fibers are characterized by the facts that they are insoluble in and unaffected by boiling water, i; .e., upon immersion in boiling water for a period often minutes the fiber shrinks less than 10% and usually less than 5%, and the loss in dry tensile strength is less than 10% and usually less than 5%. They have a work recovery at 3% elongation (as defined later) of at least 45 and usually at least 50%. Moreover, they have a characteristic internal structure, as shown by X-ray diffraction patterns, which suggests that the fibers are composed of polyvinyl alcohol crystallites in which few, if any, of the hydroxyl groups are acetalized, and of an amorphous material which is a mixture of polyvinyl alcohol and polyvinyl acetal. It is believed that the chemical structure of the aldehyde used for acetalization together with the particular fiber structure arising from the described method of preparing and processing the fiber are responsible for the high work recoveries of the yarns and the high resilience of the fabrics obtained therefrom.

Work recovery (see A Quantitative Study of Resilience, L. F. Beste and R. M. Hoffman, Textile Research Journal 20, 441 (1950)) is a measure of the tendency of a yarn to recover from deformation. In general, yarns having high work recovery yield fabrics which have high resilience. Work recovery is defined as the per cent of work recovered when a yarn is allowed to recover from a given stretch (or bend, or twist) relative to the work required to accomplish said stretch. It is measured by dividing the area under the stress-strain curve up to a given elongation, obtained when the yarn is allowed to recover, by the area under the curve obtained when the yarn is stretched, and multiplying by one hundred. It has been found that work recovery from elongation of 3% or higher correlates well with fabric resilience.

The following examples in which parts are by weight are illustrative of the invention.

Example I Oriented polyvinyl alcohol yarn was prepared as follows: A solution of 250 parts of polyvinyl alcohol of molecular weight about 27,000, 56 parts of pyridine and 2 parts of a solubilized long-chain phosphate ester in 1082 parts of water was pressure-filtered through alternate layers of cloth and cotton batting. The filtered solution was pumped with a gear pump at the rate of 2.6 ml. per minute per spinneret through 60 hole (0.004 inch hole diameter) spinnerets into a 45% aqueous sodium dihydrogen phosphate coagulating bath at 28 C. The yarn travel in the coagulating bath was about 60 inches. The yarn was removed from the bath by a Godet wheel operating at a peripheral speed of 377 inches per minute. It was then stretched to a draw ratio of about 5:1 by drawing it in a boiling concentrated aqueous sodium dihydrogen phosphate solution at 103- 105 C., and wound up on a bobbin. The drawn yarn was washed with water and air-dried on the bobbin, i. e., at constant length.

Skeins of the oriented, dry yarn were immersed for 30 minutes in water at 15 C., during which treatment the yarn shrank about 40-42% of its initial (oriented) length, and the water was washed from the yarn with 2-B alcohol.

The cyclic monoaldehyde used in the acetalization step was S-(or 6-)hydroxyoctahydro-4,7-methanoindene-l-(or 2-)carboxaldehyde. This compound, which has the formula -HO I CHOH HO- i H H2 H- I CHO u/ s H CH2 and is prepared by hydrocarbonylation of dicyclopentenyl alcohol, is described and claimed in application Ser. No. 295,567, filed by E. T. Cline on June 25, 1952. Because of the reactivity of the two substituents in acetal forma- 7 tion, this compound is presumed to be an equilibrium mixture of the hydroxyaldehyde with interpolyhemiacetals, of the formula X being the number of repeating units. The equilibrium mixture has a cryoscopic molecular weight (determined in dioxane) of about 319, the molecular weight of the monomeric hydroxyaldehyde being 180.

The skeins were immersed for minutes in about 25 parts per part of fiber of an acetalization mixture maintained at 125 C. and consisting of 45 parts of S-(or 6-)hydroxyoctahydro-4,7-methanoindene-1-( or 2-) carboxaldehyde, 8 parts of 92% phosphoric acid, 3.5 parts of 2,5-diethoxytetrahydrofuran (as the difunctional aldehyde precursor), 7.5 parts of water and 192 parts of diethylene glycol. The treated yarn was then washed successively with 2-B alcohol, 5% aqueous sodium bicarbonate solution and water. The skeins were then boiled OK for one hour at 100 C. in an aqueous solution containing 0.1% of sodium carbonate and 0.1% of a commercial fatty alcohol sulfate detergent, rinsed in water and dried in air.

The total shrinkage of the yarn during the water relaxation and acetalization treatments was 46.8%, and after the boil-off it was 47.7%, showing that "cry little shrinkage in boiling water took place after acetalization. The fibers had gained 63.7% in weight during acetalization, corresponding to acetalization of about 35% of the hydroxyl groups in the polyvinyl alcohol.

The fibers after boil-off had a filament denier of 5, a dry tenacity of 0.9 g./den. at 25% elongation, and work recoveries from 1, 3, and 5% stretch of 80, 53, and 37%, respectively.

Example II Polyvinyl alcohol yarn was prepared as in Example I except that (1) the spinning solution contained 200 parts of polyvinyl alcohol of molecular weight about 37,000, 1.8 parts of the solubilized long-chain phosphate ester and 1090 parts of water; (2) the pumping rate was 3 ml. per minute per spinneret and (3) the temperature of the coagulating bath was 45 C. a

A skein of the oriented, washed and dried yarn was immersed for 10 minutes in a mixture of parts by volume of 2*B alcohol and 45 parts by volume of water at 25 C., then rinsed with 11-13 alcohol. This treatment caused the yarn to shrink by about 38% of its oriented length.

The skein, still damp with 2-B alcohol, was immersed for 30 minutes at 130 C. in 25 parts per part of yarn of an acetalization mixture consisting of 30 parts of 5- (or 6-)hydroxyoctahydro-4,7-methanoindene-l-(or 2-)- carboxaldehyde, 5.3 parts of 92% phosphoric acid, 3.5 parts of 2,S-diethoxytetrahydrofuran, 5 parts of water and 126 parts of diethylene glycol. The yarn was then washed and boiled off as in Example I. No shrinkage occurred during the boil-off, the total shrinkage during water relaxation and acetalization being 47%. The yarn gained 65.3% in weight, corresponding to acetalization of about 35.5% of the hydroxyl groups. It had a filament denier of 4.9, a modulus of 18 g./den., and work recoveries from 3 and 5% stretch of 54 and. 36%, respectively.

Example III Polyvinyl alcohol yarn spun and stretched as in Example II was washed with water. Samples of the yarn were then relaxed 35% and 45 respectively (i. e., al-

lowed to shrink 35% and 45% of the oriented length) by running the wet yarn from one bobbin to another operated at a correspondingly slower speed. The relaxed yarns were then allowed to air-dry at fixed length.

Skeins of the relaxed, dry yarns were immersed in 25 parts per part of fiber of an acetalization mixture consisting of 60 parts of 5-(or 6-)hydroxyoctahydro-4,7- methanoindene-l-(or 2-)carboxaldehyde, 10.6 parts of 92% phosphoric acid, 3.5 parts of 2,5-diethoxytetrahydrofuran, 10 parts of water and 257 parts of diethylene glycol for 32 minutes at C. The skeins were washed and boiled off as in Example I. For each of these two yarns, the shrinkage during acetalization and boil-oil, and the weight gain and extent of acetalization is given in the following table:

Example IV Using polyvinyl alcohol having a molecular weight of about 40,000, a 1030 filament tow was spun, stretched. washed and dried as described in Example I except that the rate of delivery of the solution to the spinneret was much higher because of the greater number of holes, and that the washing and drying operations were carried out continuously while the tow was passed over suitably spaced and driven rollers.

The relaxation step was carried out by immersing a portion (A) of the tow for 10 minutes at 25 C. in a solution of 17.5 parts by volume of diethylene glycol in 82.5 parts by volume of water, wherein the tow shrank about 43% in length. This portion was then dried in air. Another portion (B) was similarly treated except that the aqueous relaxing bath contained 27.5% by volume of diethylene glycol, wherein it shrank about 30% of its length. This portion was then rinsed with diethylene glycol.

Portion A was immersed for 30 minutes at 128 C. in 25 parts per part of fiber of a solution consisting of 60 parts of 5-(or 6-)hydroxyoctahydro-4,7-methanoindene-l-(or 2-)carboxaldehyde, 10.62 parts of 92% phosphoric acid, 6.93 parts of 2,5-diethoxytetrahydrofuran, 10 parts of water and 254 parts of diethylene glycol. Portion B was similarly treated except that the acetalization was carried out at 130 C. for 44 minutes. Both portions were neutralized and boiled off as in Example I. In portion A, the total shrinkage after acetalization Was 53%, and the weight gain was 67.1%; in portion 13 the total shrinkage was 35.5% and the weight gain was 65.5%. Neither portion showed any additional shrinkage during the boil-oif. The table below shows the physical properties of the treated yarns.

Skeins of polyvinyl alcohol yarn spun, stretched, washed and dried as in Example I were immersed for 10 minutes at 25 C. in a solution containing 15% by volume of diethylene glycol and 85% by volume of water, wherein they shrank 27%. The yarn was rinsed in 2-B alcohol and allowed to dry in air.

The yarn was acetalized for 43 minutes at 136 C. in 25 parts per part of fiber of a mixture consisting of 105 parts of -(or 6-)hydroxyoctahydro-4,7-rnethanoindenel-(or 2)carboxaldehyde, 18.6 parts of 92% phosphoric acid, 10.1 parts of 2,5-diethoxytetrahydrofuran, 17.5 parts of water and 446 parts of diethylene glycol. The yarn was then neutralized and boiled 01f as in Example I. The total shrinkage after acetalization was 45%. There was no additional shrinkage during boil-off. The yarn had gained 75.5% in Weight, corresponding to acetalization of about 41% of the hydroxyl groups. It had a filament denier of 4.8, a dry tenacity of 0.85 g./ den. at 14% elongation, a modulus of 16 g./ den. and work recoveries from 3% and 5% stretch of 52% and 38%, respectively.

In addition to the cyclic monoaldehyde of the examples, which gives particularly outstanding results, there can be used in the process of this invention any monoaldehyde having at least one ring of at least five members with the aldehyde group attached directly to an annular carbon thereof. These are the aldehydes used in the process of the Cline and Stevenson application Ser. No. 142,537, now U. S. Patent 2,636,803 already referred to. It will be seen that although the process of the present application uses these same materials, they are here associated with a dialdehyde or precursor thereof, and in addition the process involves a new and specific method of relaxing the oriented polyvinyl alcohol yarn prior to acetalization. Further examples of suitable aldehydes include benzaldehyde, hexahydrobenzaldehyde, o-chlorobenzaldehyde, p-chlorobenzaldehyde, 2,4-dichlorobenzaldehyde, 3,4-dichlorobenzaldehyde, 2,6-dichlorobenzaldehyde, p-tolualdehyde, p-ethylbenzaldehyde, 2,4-dimethylbenzaldehyde, p-phenylbenzaldehyde, p-benzylbenzaldehyde, m-nitrobenzaldehyde, a-naphthaldehyde, ,fi-naphthaldehyde, 9-anthraldehyde, furfural, S-methylfurfural, thiophenaldehyde, and the like. The above-described structural requirements are based on observations which indicate that, in order to produce the new and improved fibers of this invention, it is necessary that the aldehyde group be as close as possible to the cyclic structure. This is illustrated by the fact that phenylacetaldehyde or hydrocinamaldehyde do not produce fibers having outstanding work recoveries. The presence of a ring structure is essential, as shown by the fact that acyclic aldehydes such as chloroacetaldehyde, butyraldehyde, crotonaldehyde, 3,5,5-trimethylhexanal and 2-n-propyl- 2-heptenal, when used in the process of this invention, give yarns having low work recoveries and usually also low resistance to boiling water. Formaldehyde gives poor resilience, i. e., inferior work recovery from 3% elongation.

Of the aldehydes defined above, the preferred ones are those which contain up to 20 carbon atoms, for the reason that higher molecular weight materials tend to give yarns of increased plasticity and increased sensitiveness to organic solvents. The most useful compounds are the aldehydes of five to eleven carbon atoms having the aldehyde group attached to a nuclear carbon of a ring of five to six annular atoms, and in particular those a1- dehydes containing only carbon, hydrogen and oxygen. Excellent results are obtained with benzaldehyde, hexahydrobenzaldehyde, furfural and 5-(or 6-)hydroxyoctahydro-4,7-methanoindene-1-(or 2-)carboxaldehyde, particularly with the last named compound. In all cases, the monoaldehydes can be used as such or as their acetals, preferably with alkanols of one to two carbon atoms. In particular, the last named compound, as already mentioned, is believed to exist partly in the form of an interpolyhemiacetal. It can also be used as the acetals with alkanols, e. g. methanol or ethanol.

Aldehydes within the defined class may vary rather widely in activity. Certain aldehydes may be relatively unreactive, for example because of steric hindrance caused by multiple or heavy substitution on the carbons adjacent or near to the carbonyl group. Due allowance must be made for such variations in reactivity, which will be apparent to the skilled chemist.

Suitable dialdehydes, used as such or as their precursors, are those containing at least three carbon atoms, inclusive of the carbonyl carbons, i. e., those in which the aldehyde groups are separated by at least one carbon atom. The most easily accessible, and therefore preferred, dialdehydes are those which have from one to four carbon atoms between the aldehyde groups and a total of three to ten carbon atoms and which, apart from the carbonyl oxygens, contain only carbon and hydrogen. Among the suitable aldehydes may be mentioned malondialdehyde, succinic dialdehyde, glutaric dialdehyde, adipic dialdehyde, phthalic dialdehyde and terephthalic dialdehyde. Particularly preferred are the saturated aliphatic dialdehydes of three to five carbon atoms which, apart from the carbonyl oxygens, are hydrocarbon.

It is preferred to use these dialdehydes in the form of their acetals, as these compounds are more stable than the free aldehydes and give excellent results. Suitable acetals include not only the usual open chain tetraalkyl (e. g. tetramethyl or tetraethyl) acetals but also the cyclic anhydrides of dihemiacetals of dialdehydes. Such compounds open readily to give the corresponding open chain dialdehyde. Examples of such alpha,omega-dialkoxy cyclic ethers are 2,5-dimethoxyand 2,5-diethoxytetrahydrofuran (see U. S. 2,465,988), which are particularly useful in this process.

The yarns obtained in accordance with this invention are particularly useful in the manufacture of fabrics for wearing apparel, curtains, drapes, blankets, etc., in view of their great resilience and of their insensitivity toward boiling water and dry-cleaning solvents. They are also useful in many other applications such as the manufacture of filter cloths, awnings, tents, wrapping material, etc.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious modifications will occur to those skilled in the art.

What is claimed is:

1. In a process for the preparation of oriented polyvinyl alcohol fibers of desirable water resistance, the steps which comprise (a) shrinking the oriented unrelaxed fiber by contact with a homogeneous aqueous bath having no solvent action and no appreciable softening action on the fiber and having at least 30% water content at a temperature within the range 0-50 C. and for a time within the range from three seconds to twenty minutes until the filament shrinks between 25 and 50% of its original oriented length and (b) thereafter reacting the fiber at a temperature within the range from 50 C. to just below the decomposition temperature of the reactants, with a mixture of a cyclic monoaldehyde containing only hydrogen, oxygen, and up to twenty carbon atoms and having the aldehyde group directly attached to annular carbon of a ring of at least five atoms with from 3 to 20%, by weight of said monoaldehyde, of a dialdehyde containing only hydrogen, carbonyl oxygen, and three to ten carbon atoms with at least one carbon atom between the aldehyde groups until at least 25% of the hydroxyl groups of the fiber are acetalized, the reaction of said aldehyde mixture with the fiber being conducted in a carbonyl-free liquid organic solvent for the aldehyde mixture which is a nonsolvent for the fiber and contains not more than 10% water.

2. In a process for the preparation of oriented polyvinyl alcohol fibers of desirable water resistance, the steps which comprise (a) shrinking the oriented unrelaxed fiber by contact with a homogeneous liquid aqueous medium having no solvent action and no appreciable softening action on the fiber and having at least 30% water content, containing a water-miscible liquid of one to ten carbons at a temperature, within the range 0-50 C. for

a time, within the range from three seconds to twenty minutes, sufficient to shrink the fiber between 25 and 50% of its original oriented length and (b) thereafter reacting the fiber at a temperature within the range from 50 C. to just below the decomposition temperature of the reactants, with a mixture of a cyclic monoaldehyde containing only hydrogen, oxygen, and up to twenty carbon atoms and having the aldehyde group directly attached to annular carbon of a ring of at least five atoms with from 3 to 20%, by weight of said monoaldehyde, of a dialdehyde containing only hydrogen, carbonyl oxygen, and three to ten carbon atoms with at least one carbon atom between the aldehyde groups until at least 25% of the hydroxyl groups of the fiber are acetalized, the reaction of said aldehyde mixture with the fiber being conducted in a carbonyl-free liquid organic solvent for the aldehyde mixture which is a nonsolvent for the fiber and contains not more than water.

3. In a process for the preparation of oriented polyvinyl alcohol fibers of desirable water resistance, the steps which compare (a) shrinking the oriented unrelaxed fiber by contact with a homogeneous liquid aqueous medium having no solvent action and no appreciable softening action on the fiber and having at least 75% water content at a temperature of 0 to 50 C. for a time, within the range from three seconds to twenty minutes, sufficient to shrink the fiber between 25 and 50% of its original oriented length and (b) thereafter reacting the fiber at a temperature within the range from 50 C. to just below the decomposition temperature of the reactants, with a mixture of a cyclic monoaldehyde containing only hydrogen, oxygen, and not more than twenty carbons, having the aldehyde group directly attached to annular carbon of a ring of at least five atoms with from 3 to by weight of said monoaldehyde, of an acetal of a dialdehyde containing only hydrogen, carbonyl oxygen, and three to ten carbon atoms with at least one carbon atom between the aldehyde groups, until at least of the hydroxyl groups of the fiber are acetalized, the reaction of said aldehyde mixture with the fiber being conducted in a carbonyl-free liquid organic solvent for the aldehyde mixture which is a nonsolvent for the fiber and contains not more than 10% water.

4. In a process for the preparation of oriented polyvinyl alcohol fibers of desirable water resistance, the steps which comprise (a) shrinking the oriented unrelaxed fiber by contact with a homogeneous liquid aqueous medium having no solvent action and no appreciable softening action on the fiber and having at least 75% water content at a temperature of 0 to 50 C. for a time, within the range from three seconds to twenty minutes, sufiicient to shrink the fiber between 25 and 50% of its original oriented length and (b) thereafter reacting the fiber at a temperature within the range from 50 C. to just below the decomposition temperature of the reactants, with a mixture of a cyclic monoaldehyde containing only hydrogen, oxygen, and five to eleven carbons, having the aldehyde group directly attached to annular carbon of a ring of five to six annular atoms, and containing only carbon, hydrogen, and oxygen with from 3 to 20%, by weight of said monoaldehyde, of a dialdehyde containing only hydrogen, carbonyl oxygen, and three to ten carbon atoms with at least one carbon atom between the aldehyde groups until at least 25 of the hydroxyl groups of the fiber are acetalized, the reaction of said aldehyde mixture with the fiber being conducted in a carbonyl-free liquid organic solvent for the aldehyde mixture which is a nonsolvent for the fiber and contains not more than 10% water.

5. In a process for the preparation of oriented polyvinyl alcohol fibers of desirable water resistance, the steps which comprise (a) shrinking the oriented unrelaxed fiber by contact with a homogeneous liquid aqueous medium having no solvent action and no appreciable softening action on the fiber and having at least water content at a temperature of 0 to 50 C. for a time sufiicient to shrink the fiber between 25 and 50% of its original oriented length and (b) thereafter reacting the fiber at a temperature within the range from 50 C. to just below the decomposition temperature of the reactants, with a composition essentially comprising a mixture of cryoscopic molecular weight in dioxane of the order of about 319, of hydroxyoctahydro-4,7-methanoindene carboxaldehydes of the formula H C H CH/ \C-CH and the interpolyherniacetals ort l 0(l OH-CH -o-- H H: rr-- --onon H on n C a X thereof, X being the number of repeating units, together with from 3 to 20%, by weight of said mixture, of 2,S-diethoxytetrahydrofuran until at least 25% of the hydroxyls of the fiber are acetalized, the reaction of said aldehyde mixture with the fiber being conducted in a carbonyl-free liquid organic solvent for the aldehyde mixture which is a nonsolvent for the fiber and contains not more than 10% water.

6. An acetalized oriented polyvinyl alcohol fiber as produced by the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,360,477 Dahle Oct. 17, 1944 2,3 87,831 Cogan et al. Oct. 30, 1945 2,399,401 Sonnichsen et al Apr. 30, 1946 2,636,803 Cline et al Apr. 28, 1953 2,63 6,804 McClelland et a] Apr. 28, 1953 

1. IN A PROCESS FOR THE PREPARATION OF ORIENTED POLYVINYL ALCOHOL FIBERS OF DESIRABLE WATER RESISTANCE, THE STEPS WHICH COMPRISE (A) SHRINKING THE ORIENTED UNRELAXED FIBER BY CONTACT WITH A MONOGENEOUS AQUEOUS BATH HAVING NO SOLVENT ACTION AND NO APPRECIABLE SOFTENING ACTION ON THE FIBER AND HAVING AT LEAST 30% WATER CONTENT AT A TEMPERATURE WITHIN THE RANGE 0*-50* C. AND FOR A TIME WITHIN THE RANGE FROM THREE SECONDS TO TWENTY MINUTES UNTIL THE FILAMENT SHRINKS BETWEEN 25 AND 50% OF ITS ORIGINAL ORIENTED LENGTH AND (B) THEREAFTER REACTING THE FIBER AT A TEMPERATURE WITHIN THE RANGE FROM 50* C. TO JUST BELOW THE DECOMPOSITION TEMPERATURE OF THE REACTANTS, WITH A MIXTURE OF A CYCLIC MONOALDEHYDE CONTAINING ONLY HYDROGEN, OXYGEN, AND UP TO TWENTY CARBON ATOMS AND HAVING THE ALDEHYDE GROUP DIRECTLY ATTACHED TO ANNULAR CARBON OF A RING OF AT LEAST FIVE ATOMS WITH FROM 3 TO 20%, BY WEIGHT OF SAID MONOALDEHYDE, OF A DIALDEHYDE CONTAINING ONLY HYDROGEN, CARBONYL OXYGEN, AND THREE TO TEN CARBON ATOMS WITH AT LEAST ONE CARBON ATOM BETWEEN THE ALDEHYDE GROUPS UNTIL AT LEAST 25% OF THE HYDROXYL GROUPS OF THE FIBER ARE ACETALIZED, THE REACTION OF SAID ALDEHYDE MIXTURE WITH THE FIBER BEING CONDUCTED IN A CARBONYL-FREE LIQUID ORGANIC SOLVENT FOR THE ALDEHYDE MIXTURE WHICH IS A NONSOLVENT FOR THE FIBER AND CONTAINS NOT MORE THAN 10% WATER. 